1. Field of the Invention
The present invention relates to a recording medium capable of providing a recorded image with an excellent light transmittance in a method of image formation using an electrostatic recording system. More particularly, the present invention concerns a recording medium which provides a high-quality clear image in methods of image formation using recording tools such as felt-tip pens, fluorescent markers, and fountain pens employing a water-based medium, as well as a recording apparatus such as a pen plotter or an ink-jet recording system.
In addition, the present invention concerns a recording medium which provides a high-quality image in a thermal transfer recording system or an impact-type recording system.
2. Description of the Related Art
A method of image formation by an electrostatic recording system is a system whereby, using various methods, an image is formed by selectively imparting a charge to the surface of a recording medium and by causing a particulate recording agent (toner) to adhere to the charged portions thereof. This method is employed in copying machines, facsimile apparatuses, and the like. In particular, copying machines of an electrophotographic system using an electrostatic process have been used widely.
The method of image formation based on the electrostatic recording system comprises a process of forming an image on a recording medium by means of charges and a process of thermally fixing an adhered recording agent. As properties required of a recording medium suitable for the electrophotographic system, for example, it is possible to cite electrical conductivity, smoothness, whiteness, gloss, lack of curling, uniform quality, and so forth. Among these items, the electrical characteristics of the surface of the recording medium are particularly important. For this reason, a recording medium for electrophotography is generally processed to give it a suitable surface resistance.
In addition, there is also strong demand for a recording medium which transmits light and can be used in an optical apparatus (e.g., an overhead projector) to observe a transmitted image. Such a recording medium must have an outstanding degree of light transmittance in addition to the aforementioned property requirements.
As recording media for the above-mentioned application, light-transmissive sheets, such as plastic films whose surfaces have been processed for electric conductivity, are generally used. In this case, however, the recording medium itself, including its surfaces, must have a sufficient heat resistance, in addition to the aforementioned requirements.
Furthermore, there is also strong demand for color images in applications such as those described above.
In order to form a color image on a light-transmissive sheet, a method of silver-halide photographic printing or electrophotography has hitherto been used, but, in both cases, a large-scale apparatus is required.
As the most simple method of forming a color image, it is possible to cite a directly coloring method by so-called water-based ink pens, using the water-based ink of felt-tip pens, fluorescent markers, fountain pens, or the like, or a method based on a pen plotter making use of such pens. In this case, the light-transmissive material is required to enable the recording agent contained in the ink to be fixed promptly thereon.
As another method of forming a color image, it is also possible to cite one using a printer or plotter making use of a color hard-copy machine, a wire dot method, an ink jet method, a thermosensitive recording method, or the like.
In this case, the light-transmissive recording material is required to exhibit the properties given below.
For instance, in the case of the ink-jet recording system using water-based ink, speedy fixing characteristics of the recording agent of the ink are required, in the same way as with water-based ink pens, while, in the case of the thermal transfer recording system, smoothness and heat resistant characteristics are particularly important.
As described above, requirements concerning the properties of recording media vary, and a light-transmissive recording medium which can be used in all of the aforementioned recording systems (those using a copying machine of the electrophotographic system, water-based ink pens, the ink-jet recording system, the wire dot printing system, or the thermal transfer recording system) has not yet been found.
For example, the overhead projector (OHP) film for electrophotography disclosed in U.S. Pat. No. 4,370,379 is arranged such that an subbing layer having a surface resistance of 1.0.times.10.sup.6 to 9.0.times.10.sup.9 .OMEGA. is provided on a plastic film, and a toner-receiving layer having a surface resistance of 1.0.times.10.sup.10 to 1.0.times.10.sup.13 .OMEGA. is further provided thereon.
Although this film has sufficient heat resistance and surface conductivity, the surface of the film per se is nonporous, so that, if coloring is effected on an image obtained by an electrophotographic copying machine, using a felt-tip pen, a fluorescent marker, a fountain pen, or the like, an aqueous component remains on the surface, and drying is therefore delayed. Consequently, there is a drawback in that the image may be impaired if something comes into contact with its surface after recording.